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Restoring a Soarmaster

Hi there,

I'm new to the forum and posting for the first time.

I was one of the 'early birds' of the ultralight development. I foot-launched a rogallo powered by a Soarmaster power unit for a couple of years in the late 70's and early 80's -- logging about 150 to 200 hours of foot-launched power airtime before quitting. I still have a 1978 rogallo wing and a 1978 soarmaster power unit stored in a relative's attic on the far side of the country. I am considering restoring this combination to flyable condition.

Restoration will be mostly about the engine and transmission of the power unit. Are there any old Soarmaster pilots out there? Or anyone familiar with the mechanical details of that power unit? I'd love to ask some questions.

Any leads to further information regarding the Soarmaster power unit will be appreciated.

The Soarmaster is a basic system. Any two cycle repair knowledge should get the engine running. Extension shaft may need a new bearing or flex coupling if it even has one. Again should not be much of a problem.

I have not had a Soarmaster so am not the person you are seeking but I will say forget the old Rogallo and pare it with a modern hang glider. Keep the old wing for the type of flying it was intended for. My understanding is the Soarmaster/Rogallo had some safety issues. Probably a good thing you quit when you did. Even with a new wing be careful out there and understand tumbles and power pushovers. It is nice to see some of those old systems come back to life when done safely.

Prop Warning...

Originally Posted by jedi

The Soarmaster is a basic system. Any two cycle repair knowledge should get the engine running. Extension shaft may need a new bearing or flex coupling if it even has one. Again should not be much of a problem.

I have not had a Soarmaster so am not the person you are seeking but I will say forget the old Rogallo and pare it with a modern hang glider. Keep the old wing for the type of flying it was intended for. My understanding is the Soarmaster/Rogallo had some safety issues. Probably a good thing you quit when you did. Even with a new wing be careful out there and understand tumbles and power pushovers. It is nice to see some of those old systems come back to life when done safely.

I had a twin-engine Soarmaster system on a Vector 600 in 1982. It had 2 West Bend engines with centrifugal clutches & chain drive in an oil bath sump that mounted the drive shaft. The prop on that system used 2 metal blades bolted to an Aluminum hub. The entire set up seemed bush league to me so I took it off a put it on a powered ice boat. Shortly thereafter, the prop threw a blade which miraculously didn't kill anyone. The bad part is that the new system I replaced it with on the Vector had a torsional drive shaft failure & I broke my back in the crash. Drive shafts (with a single cyl. engine pumping against a prop) are always a bad idea. This is especially true if there is no torsional dampener & the sprocket or pulley just has a bolt thru the shaft.

Watch your toes... didn't they call those things the "Sawmaster" back in the day?

Though I shouldn't talk... in a brief moment of madness a few years ago I restored and flew an old Quicksilver weightshift with a 15HP Yamaha engine. Never tried to foot launch it, did a bunch of crow hops and then crashed it into a hangar roof on my first trip around the pattern. Wasn't hurt too bad, but needed a cane for several months...

Putting any high thrustline power unit on a modern flexwing or an Atos type glider would be a very bad idea. Modern wings have very little pitch damping (not to be confused with pitch stability -- stability and control damping are different things). With a high thrustline you want heavy pitch damping -- which my old '78 glider has in abundance. Likewise for yaw damping because the soarmaster unit puts the propeller disk some distance behind the center of mass of the system. In certain flight situations the disk can use the propshaft as a lever arm and 'walk' the nose around in yaw, which initiates a cascade of very negative events. I personally experienced this cascade multiple times in different 'glider + powerunit' combinations, and some of these combinations were truly horrifying in their instability under full throttle. I also personally witnessed two fatal accidents that began with these cascades. The gliders in these events were always the ones with the least damping in pitch, roll, and yaw.
The '78 wing I have in storage was intended to be a trainer/entry-level glider, and has massive damping on all three axis. More damping than any modern wing. This would make it a lousy mountain glider, but it worked great under full power soarmaster.

The original Eagle canard ultralight of 1980 came with these double soarmaster units, and I witnesses one of those early unit propellers blow up during a full throttle ground run-up. Those double units had numerous vibration issues and were soon discontinued.
I did have one Soarmaster unit fail the driveshaft in flight. A textbook torque failure of the long tubular shaft. This occured at a bearing due to the bearing beginning to seize up and so concentrating torque stress there. I was at 2000 feet, so it was no big deal. I chose a landing field, set up an approach and landed with no incident. Remember that the wing is a glider first, and the soarmaster is just an auxilary addition. When the unit fails, you still have a glider.

I personally witnessed one of these accidents. It was during the take-off run. The pilot lost his three smallest toes off one foot. He soon learned how to walk and run without them, and then continued flying.

When ordering a power unit from Soarmaster Inc., you had the option of dictating the total length of the unit. A longer unit would weigh a little bit more -- but would put the propeller disk out of reach of your feet. The length of my unit was dictated by the worst case scenario I could model for the rearward stretch of my feet. So I never had any problems with this.

I flew one of the original weight-shift Quicksilver/Yamaha units back in the early spring of 1980. They had just released it for sale, and the shop I worked for was going to be a dealer. I liked the climb rate (compared to a 9 hp soarmaster), and the wheels made take-offs and landings a breeze. But on the negative side, the wheels were too small in diameter to handle the rough Texas cow pastures we were flying from, and the glide and sinkrate with power off was really frightening, from my point of view as an experienced HG pilot --- this thing was NOT a glider, and you'd better have an open field under you at all times, because when the yamaha quits you are going DOWN right NOW.
I also flew the Wizard W1 model, which was mostly a clone of the quicksilver, but it had 15 inch diameter wheels with nylon spokes. This worked really well in our cow pastures, and I preferred the Wizards over the Quicks -- but the terrible glide and sinkrate with power off remained.

Thanks for post #5. Looks like you know what you are doing. Specifically what wing is that? What company were you with (Texas)?

More details on "In certain flight situations the disk can use the propshaft as a lever arm and 'walk' the nose around in yaw, which initiates a cascade of very negative events." Is this a dynamic yaw roll coupling issue?

Would the long shaft and a rear aerodynamic surface(s) add the required damping to a modern glider design with an extended keel?

I am thinking an inverted V tail with 1" OD x 0.053 wall leading edge for damping and prop protection.

Thanks for post #5. Looks like you know what you are doing. Specifically what wing is that? What company were you with (Texas)?

More details on "In certain flight situations the disk can use the propshaft as a lever arm and 'walk' the nose around in yaw, which initiates a cascade of very negative events." Is this a dynamic yaw roll coupling issue?

Would the long shaft and a rear aerodynamic surface(s) add the required damping to a modern glider design with an extended keel?

I am thinking an inverted V tail with 1" OD x 0.053 wall leading edge for damping and prop protection.

I own a 1978 Seahawk 190, made by Seagull Aircraft in California.
Our 1980 business was "Ultralight Power Gliders" of Houston, Texas. The original building was very close to the Houston Astrodome south of downtown.

In '79 and '80 there were several of us flying soarmaster and when we began to experience and witness these incidents we talked a lot about it, having a variety of theories. We came up with a propeller behavior that we called the 'Paddle-wheel Effect'. The idea being that the prop. disk is very close behind the trailing edge of the wing. The top half of the disk is working air that flows off the top of the wing, and the lower disk half in air off the lower surface. When you begin to stall the wing the upper half is in disturbed, turbulent air while the lower half is in compressed laminar flow. The lower disk half is getting much better 'traction' than the upper. One effect would be that the prop. would walk sideways like the paddle-wheel of an old steamboat. On the soarmaster, the prop. would walk to the pilot's left, and it's behind the wing - so the left wing is yawing forward ( the nose is swinging right). At the same time the ever-present torque of the unit is trying roll the right wing down. The yawing and rolling combine in a bad way -- they amplify one another.
You end up having swung 90 degrees to the right of your original heading while also rolling 90 degrees right. You are now pointed vertically down at the ground and the wing goes negative until the tips and luff-lines engage ( you have now gone weightless and your hang strap is loose). The tips and luff-lines will prevent a complete inversion -- but as long as you maintain full throttle the wing will NOT pull-out, and will accelerate in a true vertical dive until you drop the throttle (it's in your mouth) or impact the ground vertically. If you do drop throttle -- the torque and paddle-wheel effect instantly disappear as does the thrust that maintains the dive. You've got a pure HG again and it will proceed to pull out of the inversion and the dive with great gusto. You will have to work hard to prevent it from zooming up into a whipstall. I actually experienced all of this more than once. The pull-out was the highest G force I ever experienced as a pilot and was followed by two successive whip-stalls before I could bleed off all that energy.

We knew that it was occurring during a stall at full thrust, and that the glider yawed and rolled simultaneously, always to the right, and that we ended up pointed straight down, straps loose and accelerating.
All the stuff about the Paddle-wheel effect is our speculation and theory - trying to understand the thing - and was there a solution?

My solution was to never even approach stall speed when under power - not EVER.

And to always EXPECT something to go wrong at any instant when under power.

And to instantly spit out that throttle if anything felt even the slightest bit strange or 'off'.

And to never allow the right wingtip to go below the horizon when under power -- all powered turns are to the left, never right. If this thing happens when you are banked left, it first rolls/yaws the wing out of the turn back to level - giving you time to wake-up and spit out the throttle.

The answer to every soarmaster problem is to spit out the throttle.

The high thrustline power unit is NOT YOUR FRIEND.

The soarmaster concept had a lot of issues and limitations. But once I had found all the boundaries of those limitations, and operated WITHIN those boundaries, I racked up hundreds of hours of incident-free airtime. And I very much enjoyed flying that way. But I wish that I , and the others, had not had to learn those boundaries via the 'school of hard knocks'. The unit manual didn't mention any of this stuff, and no magazine article or review ever mentioned any of it either.

I really can't recommend a high thrustline on a modern glider. You would have to ruin the good qualities of the wing in order to make it safe enough for the power unit. For the tail idea, you would have to test the glider with the tail first (no power unit) to make sure it is not messing with the behavior of the wing and creating problems of it's own.
I suspect that a high thrustline only works well when you have a full-size proper tail BEHIND the prop. Like the Quicksilver or Aero103

While every aircraft has individual differences by additional counter measures. Tail size distance from wing etc. Do all pusher aircraft share these adverse effects in the same way ? While one aircraft may be more or less susceptible. Would they suffer from trying to push against the drag force resistance rather than as a tractor aircraft pulling through a drag force. The processions you describe are they enhanced by pushing VS pulling ?

I am struggling to understand what caused my plane to crash . Did I violate a never do this kind of thing as you described. It is possible that what you described coupled with a wind direction was the cause.